1. Field of the Invention
The present invention is directed generally toward diagnostic equipment and, more specifically, to a method and system for diagnosing a test system for malfunctions when a tested quantity falls outside of a range of expected values.
2. Description of Related Art
Electronic test units often measure multiple electronic properties of signals conducted by circuits provided to a device under test (“DUT”). Measuring a plurality of electrical properties of a DUT with a common test system provided with a plurality of source/measurement units (“SMUs”) eliminates the need for transporting the DUT to different test systems at various locations to complete each of the desired measurements. Sophisticated systems commonly include dedicated circuits for receiving each signal from the DUT and conducting the different measurements located at a common test station.
While such sophisticated test systems simplify the process for conducting multiple measurements on the same DUT, their complexity makes it difficult to pinpoint the possible cause of an errant measurement. Upon taking a measurement that falls outside of a range of expected values many conventional test systems merely return the outlying measurement, leaving it to a human operator to manually determine whether the errant measurement resulted from a faulty DUT, a problem with a portion of the test system, or any one of many other possible causes.
Other test systems allow an operator to manually initiate, or periodically initiate on regular intervals a global diagnostic procedure to be carried out by the test system to determine if the test system, or a portion thereof, is experiencing any problems that could cause an errant measurement result. Routinely conducting a global diagnostics routine on the test system both minimizes the risk of a faulty DUT passing the tests conducted thereon, and minimizes the waste resulting from erroneous failures of DUTs caused by a malfunctioning test system. Such global diagnostic procedures step through a predetermined diagnostic routine that checks the operation of all the various circuits of the test system provided for conducting different measurements in an effort to locate the cause of the errant measurement. However, during such diagnostic routines the test system relies on an internal or external signal generator that generates a dedicated test signal having known properties to be measured by the various different circuits of the test system. If the measured properties do not fall within a predetermined tolerance of the test signal's known properties it is concluded that a portion of the test system is malfunctioning. But to conduct such a global diagnostic routine the test system must be taken out of service, at least temporarily until the diagnostic routine is complete, before testing of DUTs can resume. Because global diagnostic routines are lengthy, conducting such global diagnostics often leads to expensive downtime that slows quality control and production of electronic components. But not conducting global diagnostics frequently enough can allow a malfunction of the measurement instrument to go undetected for significant periods of time, possibly allowing defective DUTs to erroneously pass testing.
Accordingly, there is a need in the art for a method and system for minimizing the time required for diagnosing a test system to determine whether a possible malfunction exists. The method and system can diagnose possible problems with the test system, or a portion thereof, based at least in part on an experimental measurement performed on electric signals conducted by a device under test under normal testing conditions, and can optionally focus the scope of diagnosing possible malfunctions to electric circuit components of the measurement instrument involved in conducting the experimental measurement when the existence of a possible malfunction is discovered.